1. Field of the Invention
The present invention relates to the washing of semiconductor wafers during the manufacturing of semiconductor devices. More particularly, the present invention relates to a method of and apparatus for drying wafers at the end of a wet-wash process carried out in the course of semiconductor fabrication.
2. Description of the Related Art
During the fabricating of semiconductor devices from silicon wafers, the wafers are exposed to and contaminated by various particles or chemicals. As the integrated circuits of semiconductor devices become smaller and more highly integrated, contaminants as small as about 0.1 xcexcm in diameter can now affect the operability of the semiconductor devices. Therefore, it is very difficult to keep the wafers sufficiently clean.
Today, the cleaning of the wafers accounts for approximately 30xcx9c40% of the total manufacturing process. The cleaning process thus continues to grow in importance as the design rule of the semiconductor devices decreases.
FIG. 1 shows a drying system 50 of a conventional wet station for cleaning wafers. As shown in FIG. 1, the drying system 50 comprises a loader 32, a process bath 14, a lid 40, an unloader 34, and an unloading stage 18. The arrows (solid lines) designated by reference numeral 36 represent the path along which elements holding the wafer are moved through the system 50. On the other hand, the arrows (dotted lines) designated by reference numeral 38 represent the path along which the elements are moved through the system 50 after leaving the wafer off at some point in the station.
More specifically, the loader 32 transfers a wafer 31 from a wash bath 12 to the process bath 14. The washing of the wafer in the wash bath 12 constitutes the final phase of a wet-wash process.
The process bath 14 serves to rinse the wafer 31. To this end, the process bath comprises a tub of deionized water 15. The process bath 14 also comprises a lift or elevator 13 for moving the wafer 31 into/out of the tub, and an outlet valve 19 for discharging the deionized water 15 from the tub.
The lid 40 is positioned above the process bath 14. The lid 40 comprises a gas distributer (not shown). A dried gas such as nitrogen or IPA (isopropyl alcohol) is blown onto the wafer 31 through the gas distributer to dry the rinsed wafer.
The unloader 34 transfers the wafer 33 from the elevator 13 to the unloading stage 18. At this time, the wafer 33 has already finished drying on the elevator 13. A carrier 17 for receiving the wafer 33 is positioned under the unloading stage 18. When a predetermined number of the wafers 33 have been moved onto the unloading stage 18, the unloading stage 18 containing the wafers 33 is lowered into the carrier 17 and the wafers 33 are thereby transferred into the carrier 17.
FIG. 2 is a flow chart of the drying process 20 carried out by the drying system 50. The drying process 20 will be described in detail below referring to FIGS. 1 and 2.
First, a wafer 31 that has already been washed in the wash bath 12 is prepared (step 21).
Next, a wafer-loading step 22 is carried out. In order to submerge the wafer 31 in the deionized water 15, first, the elevator 13 is raised above the level of the deionized water 15 (sub-step 22a). The loader 32 picks up the wafer 31 in the wash bath 12 and places the wafer 31 on the elevator 13 (sub-step 22b).
Then, the elevator 13 holding the wafer 31 is lowered into the deionized water 15. Thus, the wafer 31 is rinsed by the deionized water 15 (step 23). During this time, the loader 32 is returned to its former position.
Next, the wafer 31 is dried (step 24). To this end, the lid 40 is moved over the process bath 14 (sub-step 24a). The elevator 13 supporting the wafer 31 is raised above the deionized water 15 to a position at which the wafer 31 is covered by the lid 40 (sub-step 24b). Nitrogen or IPA gas is injected (sub-step 24c) from the lid 40 onto the wafer 31 to dry the wafer 31.
Finally, the wafer 31 is unloaded (step 25). First, the deionized water 15 is discharged from the tub of the process bath 14 by opening the outlet valve 19 (sub-step 25a). The elevator 13 supporting the wafer 31 is then lowered into the empty tub of the process bath 14 (sub-step 25b). Next, the lid 40 is returned to its former position (sub-step 25c). Subsequently, the elevator 13 still supporting the wafer 31 is again lifted above the tub of the process bath 14 (sub-step 25d). The unloader 34 picks up the wafer 31 on the elevator 13 and transfers the wafer 31 to the unloading stage 18 (sub-step 25e).
The above-described conventional drying system has a drawback in that it has a complex structure that takes a long time to carry out a cycle of operation comprising the drying process. Furthermore, the wafer is exposed to the air for a long period of time during the process. Accordingly, watermarks can readily form on the wafers.
Accordingly, an object of the present invention is to provide apparatus for drying a wafer and having a short cycle of operation.
Another object of the present invention is to provide apparatus for drying a wafer while minimizing the time that the wafer is exposed to external air.
In order to achieve these objects, the present invention provides a drying system comprising a process bath that includes a tub of deionized water and an elevator for moving the wafer from a position beneath the surface of the water to a position above the tub, a loader for transferring the wafer from a wash bath to the elevator of the process bath, an unloading stage, and a lid comprising an integrated lid body, gas distributer, wafer chuck and reciprocating drive for drying the wafer after the wafer is rinsed in the process bath and for transferring the wafer to the unloading stage.
Preferably, the lid body is transparent so that the wafer can be seen therethrough.
Another object of the present invention is to provide a method of drying a wafer in a short amount of time.
To achieve this object, the present invention provides a drying method in which a wafer is prepared for being dried after the wafer has undergone the final phase of a wash process in a wash bath, an elevator is positioned beneath the surface of rinsing liquid of a process bath, the wafer is transferred from the wash bath to the process bath, and the wafer is loaded onto the elevator while the elevator is positioned beneath the surface of the rinsing liquid. Accordingly, the wafer is submerged in the rinsing liquid without the need to mount the wafer on the elevator and then lower the elevator once the loader has arrived at the process bath.
Still further, another object of the present invention is to provide a method of drying a wafer in a short cycle and while minimizing the exposure of the wafer to external air.
To achieve this object, the present invention also provides a drying method comprising the steps of preparing a wafer for being dried after the wafer has undergone the final phase of a washing process in a wash bath, transferring the wafer from the wash bath to an elevator of a process bath, and rinsing the wafer with rinsing liquid of the process bath, moving a lid to a position above the process bath, subsequently raising the elevator to move the rinsed wafer into a cavity defined in the lid, securing the wafer to the lid, injecting a dried gas into the cavity and onto the wafer to thereby dry the wafer within the cavity, and moving the lid with the wafer secured within the cavity to an unloading stage.
Finally, another object of the present invention is to ensure that the method above provides a sufficiently large drying capacity. To achieve this object, the dried gas is injected onto the wafer within the cavity of the lid while the lid is being moved to the unloading stage.